1. Field of the Invention
The invention relates to a spark-ignited internal combustion engine and a method of controlling the spark-ignited internal combustion engine.
2. Description of the Related Art
An available spark-ignited internal combustion engine includes a variable compression ratio mechanism that changes a mechanical compression ratio, and a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, wherein during middle or high engine load operation, as a load applied to the engine decreases, the mechanical compression ratio is increased and the valve closing timing of the intake valve is retarded with an actual compression ratio kept unchanged (see Japanese Patent Application Publication No. 2004-218522).
In such an internal combustion engine, when an air-fuel ratio is changed from the stoichiometric air-fuel ratio to a lean air-fuel ratio, for example, if the amount of fuel injection is reduced, output torque rapidly decreases, and therefore torque variation occurs. In this case, it is necessary to change the air-fuel ratio so that the torque variation does not occur. However, the above-described internal combustion engine includes no leaching as to changing the air-fuel ratio so as to prevent the occurrence of torque variation.